It's because circles allow for a stagger and overlap as shown later on. It's not really possible to get the same effect from squares.

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echoangle an hour ago | parent [-]

But it seems like you only need the stagger and overlap because you’re using circles in the first place. Would it look worse if you just divided the rectangle into 6 squares without any gaps or overlap?

	▲	zestyping an hour ago \| parent \| next [-]
		My thought exactly. The sampling circles only enable you to (awkwardly) solve a problem that was fabricated by using circles in the first place.
	▲	panki27 an hour ago \| parent \| prev [-]
		I wondered the same thing, but characters usually don't reach the edges, so I guess circles fit the average character better?